Why Bhavishya Malika is a very secret book?

Naitat parasmā ākhyeyaṁ pṛṣṭaṭyāpi kathañca।
Sarvaṁ sampadyate devi devaguhyaṁ susaṁvṛtam॥

- Shrimad Bhagwat Mahapuran (8.17.20)

When the demon king Bali snatched heaven from the gods, at that time, on the advice of her husband Kashyap, mother Aditi kept a fast called ‘Payovrata’, and pleased with this, God appeared before her and promised to take incarnation as her son.

Lord Shri Krishna tells Mother Aditi, do not tell this secret to anyone because the words of the gods should always be kept secret, only then their work is accomplished.

This makes it clear that the things said about the incarnation of God are extremely secret, and is known to only a few people by the will of God.

Even in the Dwapar Yug, when Lord Shri Krishna appeared, only a few people of Braj could recognize him as God.

Brahma himself, fascinated by his Maya, took away the cowherd boys along with their cows just to identify whether he was God.

Today, the foolish humans of Kaliyug argue, that they need to know and understand these extremely secret mysteries of God. Only devotees chosen by god himself get to know these things when the correct time comes and they believe it.